The physical core is crystallized in magnetic iron-nickel alloy-composite. The core is not hollow.

物质核心是磁性铁镍合金复合材料的结晶，其核心不是中空的。

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The physical core is crystallized in magnetic iron-nickel alloy-composite. The core is not hollow.

物质核心是磁性铁镍合金复合材料的结晶，其核心不是中空的。

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